Coronary vessels, partially occluded by plaque, may become totally occluded by a thrombus or blood clot causing myocardial infarction, angina and other conditions. A number of medical procedures have been developed to allow for the removal of plaque from vessel walls or to clear a channel through the thrombus or clot to restore blood flow and minimize the risk of myocardial infarction. Carotid, renal, peripheral, and other blood vessels can also be blocked and require treatment. For example, atherectomy or thrombectomy devices can be used to remove atheroma or thrombus. Alternatively, in percutaneous transluminal coronary angioplasty (PTCA), a guide wire or guide catheter is inserted into the femoral artery of a patient near the groin, advanced through the artery, over the aorta, and into a coronary artery. An inflatable balloon is then advanced into the coronary artery, across a stenosis or blockage, and the balloon inflated to dilate the blockage and open a flow channel through the partially blocked vessel region. While some stenoses remain in place once dilated, others are more brittle, and may partially crack and fragment, allowing the fragments to flow downstream where they may block more distal and smaller coronary vessels, possibly causing myocardial infarction, from that site. Consequences of embolization include stroke, diminished renal function, and impairment of peripheral circulation possibly leading to pain and amputation.
Saphenous vein grafts are often used to bypass occluded coronary vessels in coronary artery bypass surgery. With time, the grafts can become occluded with grumous. The grumous can also be dilated with balloons or removed in other ways. The grumous can present an even more difficult material to remove than thrombus, as the material is very friable, and likely to break into smaller fragments during the removal procedure.
Distal embolic protection devices have been developed to prevent the downstream travel of materials such as thrombi, grumous, emboli, and plaque fragments. Devices include occlusive devices and filters. Occlusive devices, for example distal inflatable balloon devices, can totally block fluid flow through the vessel. The material trapped by the inflatable devices can remain in place until removed using a method such as aspiration. However, aspiration cannot remove large particles because they won't fit through the aspiration lumen. Also, aspiration is a weak acting force and won't remove a particle unless the tip of the aspirating catheter is very close to the particle to be removed. During the occlusion, the lack of fluid flow can be deleterious. In coronary applications, the lack of perfusing blood flow can cause angina. In carotids, seizure can result from transient blockage of blood flow. In both coronaries and carotids it is not possible to predict who will suffer from angina or seizure due to vessel occlusion. If a procedure is started with an occlusive device, it may be necessary to remove it and start over with a filter device.
Some distal embolic protection devices include filters. The filters can be advanced downstream of a site to be treated and expanded to increase the filter area. Filtrate, such as emboli, can be captured in the filter until the procedure is complete or the filter is occluded. When the capacity of the filter is reached, the filter becomes occluded, blocking fluid flow past the filter device. The filter may then be retracted and replaced or left as is. If the filter is replaced with a fresh unoccluded filter, extra wire motions are required along with extra time. While the replacement is occurring, there is a period of no embolic protection for the patient and a risk of dislodging emboli during filter manipulation. If the filter is left in place, the vessel will be occluded during the remainder of the procedure and the patient can suffer the consequences of occlusion described earlier. Both choices are less than optimal.
Another shortcoming of current filters relates to their use distal of emboli sources when the emboli sources are located immediately proximal of a vessel bifurcation or trifurcation. Multiple filters may be required, one for each vessel branch, which is cumbersome and may not be done well, if attempted at all. Further, the use of multiple filters may not be compatible with other needed equipment such as angioplasty balloons and/or stents.
Some physicians prefer to use filters while others prefer to use occlusive devices. Whether a particular procedure may call for use of an occlusive device or a filter device may not be known until midway through the procedure. Occlusive distal protection devices are generally preferred for use in carotid vessels where even tiny particles can cause big problems if they happen to lodge in a very important but small artery. However, occlusive devices compromise fluoroscopic imaging due to the lack of flow during radiopaque dye injection.
What would be desirable are intravascular filters capable of additional filtering after being occluded with thrombi, without being removed from the body. What would be advantageous are intravascular filters which can be manipulated between a filtering mode and an occluding mode. Filters that can be used in the vicinity of a bifurcation would be beneficial.